Drop math functions benchark compiled with -ffast-math

This causes undefined behavior with GCC 15 and UMESIMD,
and compilation failures with nvc++ (no support for -ffast-math).

bench/CMakeLists.txt

@@ -21,12 +21,6 @@ if(BUILD_TESTING)
   add_test(NAME bench-math COMMAND mathbench)
 endif()
 
-add_executable(mathbench-fast math_benchmarks.cc)
-target_compile_options(mathbench-fast PRIVATE
-  $<IF:$<BOOL:${MSVC}>,/fp:fast,-ffast-math>)
-target_link_libraries(mathbench-fast
-  benchmark::benchmark benchmark::benchmark_main VecCore)
-
 add_executable(quadratic quadratic.cc)
 target_link_libraries(quadratic VecCore)